1. Field of the Invention
The present invention relates to a protective semiconductor device for a secondary cell.
2. Description of the Related Art
Battery packs, which are easy to handle, have been widely used for mobile electronic devices. Such battery packs are formed of a package in which one or more secondary cells are contained. As the secondary cell, a high-capacity battery such as a lithium-ion battery, a lithium polymer battery, a nickel hydride battery, and so on is used. There is a possibility of evolution of high-temperature heat leading to ignition if an overcharge, an over discharge, an excess current, and so on are generated, since these high-capacity batteries have a high amount of energy therein.
Hence, a protective semiconductor device to prevent the occurrence of overcharge, over discharge, charge-excess current, discharge-excess current, short-circuit current, abnormal overheating, and so on is contained in the battery pack of the secondary cell. The protective semiconductor device also prevents deterioration of the secondary cell, while preventing evolution of heat and ignition from occurring by blocking the connection with the charger or the load device if necessary.
In recent years, a protective semiconductor device which protects a plurality of the secondary cells used by connecting them in series has been developed. However, in conventional protective semiconductor devices which protect the plurality of the secondary cells used by connecting them in series, there is a problem in that the a disconnection cannot be detected when generated at a part of a connection between the secondary cells and the protective semiconductor device.
In Japanese Patent Application Publication No. 2008-027658 (Patent Document 1), a method to compare a cell voltage when charge-discharge current is flowing with the one when the current is not flowing in order to detect the disconnection between the secondary cells and the protective semiconductor device is disclosed. However, by the method such as disclosed in Patent Document 1, the disconnection of the connection between the secondary cells and the protective semiconductor device which arises while using the secondary cells cannot be detected.